1. Field of the Invention
This invention relates in general to thin films for use in magnetic storage devices, and more particularly to thin film fabrication methods and even more particularly to thin film fabrication methods for increasing corrosion resistance of metallic thin film.
2. Description of Prior Art
A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer, usually called a “head” or “slider” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 (collectively “magnetic transducer elements”) travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. Typically there are two electrical contact pads (not shown) each for the read and write heads 12, 23. Wires or leads 14 are connected to these pads and routed in the suspension 13 to the arm electronics (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. The read head 12 reads magnetic transitions as the disk rotates under the air-bearing surface (ABS) of the magnetic transducer 20.
FIG. 2 is a midline section of one type of prior art magnetic transducer 20 shown prior to lapping. The substrate 43 of the slider is typically a hard durable material. The components of the read head 12 shown are the first shield (S1), surround the sensor 105 which is surrounded by insulation layers 107, 109 and the second shield (P1/S2). This type of magnetic transducer is called a “merged head” because the P1/S2 layer serves as a shield for the read head 12 and a pole piece for the write head 23. The yoke also includes a second pole piece (P2) which connects with P1/S2 at the back. The P2 curves down over coil 37 to confront the P1 across the write gap layer to form the write gap at the air-bearing surface (ABS). The zero throat height (ZTH) is defined as the point where the P2 first touches the gap layer. The sensor 105 includes a magnetoresistive material such as permalloy, but may be a multilayered structure containing various layers of ferromagnetic and antiferromagnetic material. The shields and pole pieces are ferromagnetic materials, e.g., NiFe or CoFe while ceramic materials such as TiC or AL2O3 are used for the substrate. Prior to lapping the materials and structures at the ABS extend beyond the ABS. As illustrated in FIG. 2 the material to the right of the ABS plane is removed by lapping to achieve precise control of the length of the sensor 105 (which is called the “stripe height”) and the distance from the ZTH to the ABS (which is called the “throat height”). The uncertainty of the saw plane causes variations in the stripe height which are on the order of microns and which would lead to unacceptable variations in magnetic performance if not corrected. Lapping is the process used in the prior art to achieve much tighter stripe height control in the nanometer range. In the typical process of fabricating thin film magnetic transducers, a large number of transducers are formed simultaneously on a wafer. After the basic structures are formed the wafer may be sawed into quadrants, rows or individual transducers. Further processing may occur at any or all of these stages. Although sawing has been the typical method for separating the wafers into individual sliders, recently reactive ion etching (RIE) or deep reactive ion etching (DRIE) with a flourine containing plasma has been used. The surfaces of the sliders perpendicular to the surface of the wafer that are exposed when the wafers are cut form the air bearing surface (ABS) of the slider. After lapping, features typically called “rails” are formed on the ABS of magnetic transducer 20. The rails have traditionally been used to determine the aerodynamics of the slider and serve as the contact area should the transducer come in contact with the media either while rotating or when stationary.
The metallic components of GMR heads are susceptible to corrosion both in the file environment, and during slider fabrication process. When the rows are cut from the wafer the metallic thin films are exposed and lapping is typically performed. Corrosion has typically been addressed in part by adding a thin protective layer of carbon or silicon over the films after lapping. One drawback of adding the protective layer is that it inherently adds to the spacing between the magnetic sensor and the magnetic media, since the overcoat is typically about 5–7 nm. Increased performance requires smaller sensor to media spacing and thinner overcoats which in turn decrease corrosion reliability. Elimination of the overcoat is desirable for magnetic performance, if alternatives for corrosion resistance can be found.
Not all alloys useful in magnetic heads have the same degree of susceptibility to corrosion, so it is possible to select materials with higher corrosion resistance. In U.S. Pat. No. 4,904,543 Sakakima, et al., describe the use of “nitrided-alloy” layers in magnetic thin film heads to improve resistance to corrosion and wear. A nitrogen-free Fe alloy target with or without additive elements is subjected to sputtering first in an atmosphere of Ar gas for a time sufficient to form a nitride-free Fe alloy layer on a substrate in a desired thickness and then nitrogen gas is added to a level of from 0.1 to 50% by partial pressure, so that a nitrided-alloy layer is formed on the nitride-free Fe alloy layer.
Baur, et al., have described in U.S. Pat. No. 6,436,248 the use of a barrier layer deposited on the substrate before the underlayer films to increase the corrosion resistance of metallic substrate magnetic disks. Preferably the barrier layer is deposited by medium frequency pulsed sputtering at a frequency of 10 to 200 kHz and a pulse length to pulse pause ratio from 5:1 to 1:10. Aluminum or chromium are the preferred materials for the barrier layer. Additional improvements are said to be achieved when the sputtering process gas contains a proportion of oxygen and/or nitrogen
In U.S. Pat. No. 4,130,847 Head, et al., teach the use of a layer of passivating material such as chromium which is sputter deposited over the pole tips of the transducer to prevent the corrosion of the iron-nickel alloy comprising the pole tips. A portion of the end tips of the pole pieces and the gap of the thin film inductive transducer is etched by a sputter etching process prior to deposition of the chromium.